blancmange curve

where f is the triangle curve.

The curve has been introduced by Tagaki (1903) to give an example of a curve that is nowhere derivable.

As you see the curve has the form of a pudding that has been turned on. That's why John Mills gave the curve the name of the blancmange curve (or blanc-mange curve). In fact, the 'blanc-manger' is a French kind of pudding made of almond milk and cream.

Other names of the curve are Tagaki curve, named after his introducer, and van der Waerden curve, after another (Dutch) mathematician (1930) who studied the curve.

A variation on the curve can be found for even k:

When you extend the curve to a surface, the mount Tagaki is formed.